Two former Afghan warlords have announced that they will share a ballot - one running for president, the other for vice president - in next year's elections.

Abdul Rab Rasoul Sayyaf, an influential lawmaker and religious scholar, registered his candidacy for the presidency on Thursday.

"I am hopeful that the nation will decide wisely and that their decision will lead to a prosperous future, which will ensure the honor and pride of this nation in this world and the world after," said Sayyaf.

Another former warlord, Ismail Khan, who previously has served as energy and water minister, said he will run to be Sayyaf's first vice-president in the April 5 vote.

Jan Kubis, the United Nations Secretary-General's Special Representative for Afghanistan, refused to comment on the pair's candidacy.

"It is not necessarily for me to make a judgment. The best judgment, the verdict should be should be - and I assume will be - delivered through the process of the elections," said Kubis.

Sayyaf and Khan were known warlords during the civil war from 1992 and operated until the Taliban takeover in 1996.

The election will help determine Afghanistan's future following the withdrawal of all foreign combat troops at the end of 2014.